Answer:
Continental Arctic (cA): Extremely cold temperatures and very little moisture. These usually originate north of the Arctic Circle, where days of 24 hour darkness allow the air to cool to sometimes record-breaking low temperatures. Such air masses often plunge southward across Canada and the USA during winter, but very rarely form during the summer because the sun warms the Arctic. Continental polar (cP): Cold and dry, but not as cold as Arctic air masses. These usually form farther to the south and often dominate the weather picture across the USA during winter. Continental polar masses do form during the summer, but usually influence only the northern USA. These air masses are the ones responsible for bringing clear and pleasant weather during the summer to the North. Continental Tropical (cT): Hot and very dry. They usually form over the Desert Southwest and northern Mexico during summer. They can bring record heat to the Plains and the Mississippi Valley during summer, but they usually do not make it to the East and the Southeast. As they move eastward, moisture evaporates into the air, making the air mass more like a maritime tropical air mass. Continental tropical air masses very rarely form during winter, but they usually keep the Desert Southwest scorching above 100 degrees Fahrenheit during summer.
